Synoptic characteristics of fogs over the Incheon International Airport area in Korea

Fog is a meteorological phenomenon that can be a great hazard in the airport. Incheon International Airport (hereafter IIA) is located on a partly reclaimed island on the west coast of Korea that IIA often suffers from visibility degradation due to coastal fogs and sea fogs. In order to understand the whole mechanism of the formation, the development and the dissipation of fogs, various analyses of synoptic information such as weather charts and vertical thermodynamic soundings are required. Nevertheless there have been few attempts to investigate the synoptic characteristics of the fogs over this region.

In Europe and the United States, however, such attempts had been started in the early twentieth century. Taylor (1917, Quart. J. Roy. Meteor. Soc., 43, 241-268) showed that fog is the result of cooling of low altitude air by cold sea surface, using the trajectory analyses and vertical temperature profiles. Douglas (1930, Meteor. Mag., 65, 133-135) and Lamb (1943, Meteorology Office Publication M. O. 504, 24 pp) emphasized the importance of the radiation cooling at the top of fog. Petterssen (1938, Bull. Amer. Meteor. Soc., 19, 49-55) and Leipper (1948, J. Mar. Res., 7, 337-346) showed that the inversion layer played an important role to initiate and develop the fog. In addition, Leipper (1994, Bull. Amer. Meteor. Soc., 75, 229-240) showed that it is necessary to differentiate the sea fog from the coastal fog. According to his analyses, sea fogs are associated with the relationship between the dew point temperature and the sea surface temperature while the strong inversion is a crucial factor for coastal fogs.

Based on the results from previous studies, the various physical mechanisms responsible for fog formation and maintenance over the sea can be summarized as follows:

1) At air-sea interface, air is cooled by contact with cold sea surface. After saturation, fog forms and moves with the prevailing wind. This is the mechanism of typical advection fog.

2) At coastal areas such as the U.S. west coast, the strong inversion layer over cold sea surface is generated by land breeze or warm air blowing from continent. Inversion plays an important role to restrict vertical movement of air that the air reaches saturation in the thin layer below inversion. Fog is intensified by the radiative and evaporation cooling.

3) Air reaches saturation by evaporation. This is the mechanism of typical steam fog when cold air moves over warm sea surface.

4) When a strong inversion layer is formed over warm sea surface, the instability leads to thermal buoyancy and the resultant lifting below inversion layer.

In this study, NCEP-DOE reanalysis and AWS data are used as synoptic and surface weather information, respectively. Synoptic characteristics of fog are analyzed and classified into the four mechanisms presented above, based on the classification criteria presented by Kim et al. (2006, AGU 2006 Fall meeting, San Francisco, CA, 11-15 December, 51). Except pure radiation fogs where diurnal variation of the temperature was more than 10 °C, the number of fog events formed over cold sea surface is 104 and over warm sea surface is 163 over IIA from 2001 to 2005.